Conventional vehicle side impact detection systems for triggering passive safety devices, such as an air-bag mounted in the door or seat of a vehicle or an inflatable side curtain, are normally configured to detect objects striking the front or rear doors, or the B pillar of a vehicle. Such detection arrangements typically comprise one or more accelerometers and/or pressure sensors mounted in the front or rear side doors, or in the B pillar. In particular, the zone in which impacts are detected is between the A pillar and the C pillar, and impacts occurring in this region are known as “in-zone” impacts. However, “off-zone” side impacts, involving objects striking the vehicle in front of the A pillar or behind the C pillar, may be severe, and may often not be detected by conventional side impact detectors. Thus a need exists to provide a vehicle side impact detection system that ameliorates one or more of the above problems.